Data modulation method, data modulation device and communication device

ABSTRACT

A data modulation method and a data modulation device and a communication device are disclosed. The present invention relates to the synchronization and training preamble. The reference symbol optimized in order to contain the structure of “IA-A-IA-A-A-IA-A-IA-IA” is allocated to sub-carriers of the OFDM symbol. More specifically, by designing the structure of the preamble of the time domain, distinction from the other communication system can be certainly conducted holding the correctness of the clock synchronization. Also, we have adopted the series having low peak average ratio and dynamic range of sync symbol using the OFDM. Since the generation and the detection processings can be conducted in utilizing the generation device and the detection device of the sync preamble used in the convention system, this system has an advantage in increasing the common use of the LSI chip. We have made the sync series divided into 2 parts A and B before to one B region and made this to have simple construction.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a data modulation method and a datamodulation device and a communication device, and more particularly issuitably applied to the digital communication system using such as theorthogonal frequency division multiplexing (OFDM) system to acquiresynchronism of frame and packet by using synchronizing code series(hereinafter referred to as reference symbol) when receiving signals.

2. Description of the Related Art

In recent years, with the development of OFDM digital communicationsystem, various standardization committees have been developing thestandardization of these systems. And it is expected that the OFDMsystem digital communications systems standardized by these differentstandardization committees will be used in the same frequency band mixedin the near future.

In practice, in the digital communication system of OFDM system, theInstitute of Electrical Electronics Engineers (IEEE) 802.11a formed thespecification (P802.11a/D7.0 July 1999) and has been promoting for thestandardization. And at the same time, the Broadband Radio AccessNetwork (BRAN) has formed the specification(<DTS/BRAN03003-1>V0.j(1999-09)) and has been promoting for thestandardization.

Furthermore, the High-speed Wireless Access Council/Wireless AccessGroup has already formed the specification “Multimedia Mobile AccessCommunication (MMAC) Systems specification Ver.1.1, H11.11.11 44-4” andbeen promoting for standardization, and simultaneously, the 5 GHz BandMobile Access Special Council/Asynchronous Transfer Mode (ATM) Groupforms “Multimedia Mobile Access Communication (MMAC) systemsspecification) Ver.1,1, H11.11.11 44-4” and has been working for itsstandardization.

In addition to these, presently the system to make the IEEE1394 towireless, “wireless home link” as the digital communication system ofthe OFDM system, has been under the process of standardization in Japan.

The synchronization method in the digital communication system of theOFDM system standardized by the IEEE802.11a, BRAN, High-Speed WirelessAccess Council/Wireless Access Group, and the 5 GHz Band Mobile AccessSpecial Council/ATM Group described above has been already decided.

On the other hand, although in the synchronization method in the digitalcommunication system of OFDM system using the wireless home link, thesynchronization method has not been determined, it is proposed to definethe reference symbols different from other 4 digital communicationsystems.

At this point, the structure of the conventional synchronization methodand the reference symbol will be described. In the digital communicationsystem, generally the transmitting side and the receiving side areoperating in synchronism. More specifically, it is necessary tosynchronize the timing and frequency between the transmitter and thereceiver. For example, the symbol timing of the fast Fourier transform(FFT) unit should be synchronized.

In general, in order to synchronize the symbol having the specifictiming sequence, that is the reference symbol, is to be transmitted.This reference symbol is transmitted overlaying onto the data to betransmitted.

In practice, as shown in FIG. 1, the reference symbol is interpolated tothe head of transmission frame formed of F number of symbols, i.e.,burst frame, as the head symbol and is transmitted. In this connection,guard intervals are provided between the reference symbol and the headdata symbol #1, and between each of data symbols in order thatinterference between symbols (this is expressed as intersymbolinterference, and hereinafter referred to as ISI) would not occur underthe multi-bus condition.

Then, the identification of reference symbol in the receiving side, thatis the timing in synchronism, will be determined according to thecorrelation on the time axis between the receiving signal in whichreference symbol is included and the receiving signal delayed.

The maximum value of that correlation value is used to take synchronismin order to fit to the position of the last sample of the referencesymbol as correctly as possible. In this connection, the referencesymbol is formed of a plurality of synchronization patterns (hereinafterreferred to as SP) in order to detect the maximum value of correlationvalue, and the SP appears several times in one reference symbol period.

FIGS. 2A and 2B show the construction or format of the reference symbolhaving the length N in which the SP with the length Nsp on the time axisis repeated N/Nsp times.

For example, in the digital communication system of the OFDM system, thesymbol having the desired structure can be formed effectively by inversefast Fourier transforming (hereinafter referred to as IFFT) thecoefficient of the discrete Fourier transformation (hereinafter referredto as DFT).

Accordingly, in order to form the reference symbol of the length Tshaving (N/Nsp) numbers of sync patterns to be expressed in the followingequation, it is enough to modulate DFT coefficient of every (N/Nsp)order (sub-carrier of every (N/Nsp) order in the frequency region).

$\begin{matrix}{T_{s}*\left\lbrack \frac{N_{sp}}{N} \right\rbrack} & (1)\end{matrix}$

For example, when N=64, Nsp=16, only subcarrier of ±4, ±8. . . may bemodulated.

In this connection, N shows the total number of samples in one referencesymbol, i.e., one cycle of the reference symbol, and Nguard shows thenumber of samples in the guard section inserted to prevent theinterference between symbols (ISI).

Moreover, the period of correlation window will be expressed as follows:N+N _(guard) −N _(sp)  (2)

Then, the correlation value R(i) in the time area of input data streamwill be expressed in the following equation.

$\begin{matrix}{{R(i)} = {\sum\limits_{n - 0}^{N + N_{guard} - N_{sp} - 1}{{{y\left( {i - n} \right)} \cdot y}*\left( {i - n - N_{sp}} \right)}}} & (3)\end{matrix}$As is expressed above, the correlation value is, after multiplying thereceiving signal by its conjugate complex signal, these are multipliedby the number of samples included in the correlation window.

At this point, the circuit construction for calculating the correlationvalue R(i) according to EQUATION (3) will be shown in FIG. 3. As thisFIG. 3 shows, the input data (i.e., received data) is supplied to thedelayer 81 and a multiplier 83, and the delayer 81 delays this inputdata for Nsp, i.e., 1 sync pattern, and supplies this to the conjugatecomplex function device 82.

The conjugate complex function device 82 supplies the input data delayedat the delayer 81 to the multiplier 83 searching for conjugate complexdata. The multiplier 83 multiplies the input data by the conjugatecomplex data supplied from the conjugate complex function device 82, andsupplies the resulting multiplied data to the delayer 84 and the adder85.

The delayer 84, delaying the multiplied data for the period ofcorrelation window, supplies this to the subtracter 86. This subtracter86 is supplied with output data of the adder 85, and the subtracter 86subtracts the multiplied data delayed at the delayer 84 from this outputdata, and supplies the resulting subtracted data to the delayer 87having the delay time of 1 unit. The delayer 87, delaying the subtracteddata, supplies this to the adder 85. The adder 85 adds the multiplieddata from the multiplier 83 and the subtracted data delayed at thedelayer 87 and supplies the resulting output data to the subtracter 86.

Thus, the received data is correlated with itself delayed for the periodof sync pattern. And the correlation value R(i) is accumulated duringthe period of correlation window. The maximum value of the absolutevalue (|R(i)|) of the correlation value R(i), that is the output of thesubtracter 86 is detected by the maximum value detection circuit (notshown in FIG. 3) Accordingly, the timing position of the last sample ofthe reference symbol to be received will be determined. Then, this timeinformation is used as the symbol timing signal of the receiver.

In this case, the value of correlation R(i) expressed by theaccumulation value shown in EQUATION (3) will become the maximum at acertain position to be described later. And by detecting the maximumvalue, the correct symbol timing in the receiver will be determined. Inthis connection, the detection of the maximum value of correlation valueR(i) is conducted only by the reference symbol.

Furthermore, the determination whether the current symbol is thereference symbol or not is conducted based on the predeterminedthreshold value. More specifically, the maximum value of the absolutevalue |R(i)| while the absolute value |R(i)| of the correlation-valueR(i) exceeds its threshold value is taken as the detection of referencesymbol and the synchronization timing.

In this connection, the detection method of frequency offset and theeffects of phase shift are described in the Japan Patent Application No.10-330208 (Japan Patent Laid-Open No. 11-215097 bulletin) describedabove. And based on such method, the sync code series has been optimizedand being used in the conventional digital communication system.

At this point, the generation method of the conventional referencesymbol will be described in the following paragraph. All referencesymbols are generated using 64-point IFFT. There are three kinds ofcomplex number sequences in the input code sequence of IFFT, and theseare named as SA, SB and SC respectively. In this connection, contents ofSA, SB and SC will be shown in the EQUATION (4), EQUATION (5) andEQUATION (6) as follows:

$\begin{matrix}{{{SA}_{{- 26},26} = {\sqrt{\left( {13/6} \right)}*\begin{matrix}\left\{ {0,0,0,0,{S1},0,0,0,{S2},0,0,0,} \right. \\{{S3},0,0,0,{S4},0,0,0,{S5},0,0,0,} \\{{S6},0,0,0,{S7},0,0,0,{S8},0,0,0,} \\{{S9},0,0,0,{S10},0,0,0,{S11},} \\\left. {0,0,0,{S12},0,0,0,0} \right\}\end{matrix}}}{{{S1}\mspace{14mu}\ldots\mspace{14mu} 12} = \begin{matrix}{\left( {{- 1} + j} \right),\left( {1 + j} \right),\left( {{+ 1} - j} \right),\left( {{- 1} - j} \right),\left( {{- 1} + j} \right),} \\{\left( {{- 1} - j} \right),\left( {{- 1} + j} \right),\left( {{- 1} - j} \right),\left( {{- 1} + j} \right),\left( {{- 1} - j} \right),} \\{\left( {1 - j} \right),\left( {1 + j} \right)}\end{matrix}}} & (4) \\{{SB}_{26{\ldots 26}} = {\sqrt{\left( {13/6} \right)}*\begin{matrix}\left\{ {0,0,{1 + j},0,0,0,{{- 1} - j},0,0,0,} \right. \\{{1 + j},0,0,0,{{- 1} - j},0,0,0,} \\{{{- 1} - j},0,0,0,{1 + j},0,0,0,0,0,0,0,} \\{{{- 1} - j},0,0,0,{{- 1} - j},0,0,0,{1 + j},} \\{0,0,0,{1 + j},0,0,0,{1 + j},0,0,0,} \\\left. {{1 + j},0,0} \right\}\end{matrix}}} & (5) \\{{SB}_{{- 26}{\ldots 26}} = \begin{matrix}\left\{ {{+ 1},{+ 1},{- 1},{- 1},{+ 1},{+ 1},{- 1},{+ 1},{- 1},{+ 1},} \right. \\{{- 1},{+ 1},{+ 1},{+ 1},{+ 1},{+ 1},{+ 1},{- 1},{- 1},{+ 1},} \\{{+ 1},{- 1},{+ 1},{- 1},{+ 1},{+ 1},{+ 1},0,{+ 1},{- 1},} \\{{- 1},{+ 1},{+ 1},{- 1},{+ 1},{- 1},{+ 1},{- 1},{- 1},{- 1},} \\{{- 1},{- 1},{+ 1},{+ 1},{- 1},{- 1},{+ 1},{- 1},{+ 1},{- 1},} \\\left. {{+ 1},{+ 1},{+ 1},{+ 1}} \right\}\end{matrix}} & (6)\end{matrix}$

Contents of SA, SB and SC are shown as above.

The series A is the unit of the repetition of first 16 samples in theoutput signal to be put out from the IFFT when the SA is entered intothe IFFT.

Furthermore, the series B is the unit of repetition of the first 16samples in the output signal to be put out from the IFFT when the SB isentered into the IFFT.

Furthermore, the series C is the unit of repetition of 64 samples ofoutput signal to transmitted from the IFFT or 16 samples going back tothe past along the time axis from the last one of the 64 samples when SCis entered into the IFFT.

The reference symbol of each digital communication system is comprisedof the series A and series B combined.

In this connection, in IEEE802.11a, the reference symbol is formed asshown in FIG. 4, and the reference symbol shows the waveform as shown inFIG. 5. Moreover, in the BRAN for BCH, the reference symbol is formed asshown in FIG. 6, and the reference symbol shows the waveform as shown inFIG. 7. Furthermore, in the BRAN for UL, the reference symbol is formedas shown in FIG. 8, and the reference symbol shows the waveform as shownin FIG. 9. And in the high speed wireless access system (HISWAN) for UL,the reference symbol is formed as shown in FIG. 10, and the referencesymbol shows the waveform as shown in FIG. 11.

Incidentally, in order to detect the reference symbol, the syncdetection using the correlator having the construction shown in FIG. 19has been invented, not having the construction of the reference symbol.And since C region of the reference symbol is used for assuming thetransmission path, same waveform is used commonly in all digitalcommunication systems.

At this point, the amplitude of correlator output (the top stage) takesthe value from 0 to 1. The plain 1 value continues and the shape havingsharp peaks appears. However, these waveforms differ slightly from eachother. The amplitudes of the real part and the imaginary part are shownin the middle stage and the lower stage. The real part takes the valuefrom +1 to −1, and according to the combination of codes at the peakposition of the top stage, the difference of preamble occurs as shown inFIG. 15.

However, although it is difficult to differentiate between theIEEE802.11a and the UL of BRAN, the distinction between the IEEE802.11aand the BCH of BRAN is possible, and it is considered that this causesno problem. The imaginary part takes the value of 0. If the frequencydifference occurs, the imaginary part gets the value, and thus, thefrequency difference trap will be conducted to make this value 0 asdescribed in the Japanese Patent Application No. 10-330208 (Japan PatentLaid-Open No. 11-215097 bulletin).

Next, a flow of the general synchronizing operation and the OFDMdemodulation operation will be shown in FIG. 16. In FIG. 16, firstly,the existence of signal will be detected by detecting the referencesymbol. This is not only the detection of signal existence by detectingthe electric power of the received signal, but also, by detecting thesignal waveform pattern specific to the digital communication system, wecan know that the signal is the communicating party of our digitalcommunication system. Then, after the detection of reference symbol isbeing conducted, the data demodulation will be conducted according tothe OFDM system.

In the conventional digital communication system of the OFDM system,there are two problems and these will be described in the followingparagraphs.

Firstly, as the first problem supposing that the same reference symbolis used in all digital communication systems, these would not be knownas different digital communication systems after these are demodulatedby the OFDM system. Thus, this causes a problem that the wirelessterminal has to conduct the time-wasting operation.

Furthermore, in the case where the OFDM systems of different digitalcommunication systems are different systems, frames can be synchronizedbut the signal cannot be demodulated by the OFDM system. As a result,the sync signal arrived cannot be identified as to whether it is for thewireless home link or the high speed wireless access and the hang-up mayoccur.

Since such circumstance is not favorable for designing the digitalcommunication system, it is necessary to use the frame sync signaldifferent from the conventional one in the wireless home link.Similarly, regarding the packet sync signal to be used in each packet inthe frame not only to the frame sync signal, it is necessary to use thesync code series different from other digital communication systems.Thus, according to the present invention, it is necessary to construct anew sync code series that can be identified from the other digitalcommunication systems by using the same correlation circuit as before.

On the other hand, the second problem is that the lengths of referencesymbols are different. In the IEEE802.11a and BRAN, HISWAN, the lengthof one OFDM symbol is formed of 80 samples, i.e., 4 microsecond, and thelength of reference symbol is formed of an integral multiple of it, thatis, the length of reference symbol is formed of 320 samples.

However, as the length of OFDM symbol in the wireless home link, 72samples per unit is proposed. And in this case, the reference symbol isdesirable to have the integral multiple of 72 samples. For example, ifit is used for 4 symbols, it becomes 288 samples (14.4 microsecond). Ifthe conventional reference symbol is used as it is, it becomes 1.6microsecond longer, and because not only the transmission efficiencywould be decreased but also the processing cannot be conducted bydividing per one symbol, the construction of timing generation mechanismof the transmitter becomes complicated.

Accordingly, it is necessary to have the series with the length ofreference symbol 14.4 microsecond. And it is desirable that this seriescan be detected in the same correlation circuit as the conventionalcircuit because of ease of forming LSI. Since these are the digitalcommunication systems using the same 5 GHz band, it is expected todesign the common machine that can be used in a plurality of systems.

In that case, if the structures of the correlation circuits differaccording to the digital communication system to be used, the circuitsize of LSI becomes large and the unit price of the LSI will not bedecreased. And also if the common correlation circuit could be used, thesame LSI can be used when making the single mode device not only thecommon machine. And thus, it is expected that the unit price of LSI canbe lowered.

Accordingly, in the digital communication system, it is desired to havethe new reference symbols having completely different structures thatcan be detected distinguishing them from each other and having thelength of the integral multiple of 3.6 microsecond.

SUMMARY OF THE INVENTION

In view of the foregoing, an object of this invention is to provide adata modulation method and a data modulation device and a communicationdevice capable of correctly detecting sync signal of the communicationsystem in operation even when different communication systems exitmixed.

The foregoing object and other objects of the invention have beenachieved by the provision a data modulation method and a data modulationdevice and a communication device. The transmission data is encoded todata symbol, and the reference symbol in which multiple sync patterns Aand phase shifted sync pattern A, i.e., sync pattern IA, are aligned intime series in order to include the structure of“IA-A-IA-A-A-IA-A-IA-IA”, are inserted into the data symbol and the datasymbol in which the reference symbol is inserted will be modulated tothe radio frequency signal.

Thus, the receiver side can obtain the correlation detection patterndifferent from the correlation detection pattern of all conventionalsync code series because of the reference symbol.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings in which like parts aredesignated by like reference numerals or characters.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a schematic diagram showing the format of burst frame;

FIGS. 2A and 2B are schematic diagrams showing the format of theconventional reference symbol;

FIG. 3 is a block diagram showing the construction of a circuit forcalculating the correlation value;

FIG. 4 is a schematic diagram showing the construction of referencesymbol of IEEE802.11a;

FIG. 5 is a schematic diagram showing waveforms of reference symbol ofIEEE802.11a;

FIG. 6 is a schematic diagram showing the construction of referencesymbol for BCH in the BRAN;

FIG. 7 is a schematic diagram showing waveforms of reference symbol forBCH in the BRAN;

FIG. 8 is a schematic diagram showing the construction of referencesymbol for UL in the BRAN;

FIG. 9 is a schematic diagram showing waveforms of reference symbol forUL in the BRAN;

FIG. 10 is a schematic diagram showing the construction of referencesymbol for UL in the high speed wireless access system;

FIG. 11 is a schematic diagram showing waveforms of reference symbol forUL in the high speed wireless access system;

FIG. 12 is a block diagram showing the construction of a correlationdevice;

FIGS. 13A and 13B are schematic diagrams showing waveforms of thecorrelation device output with respect to each reference symbol;

FIGS. 14A and 14B are schematic diagrams showing waveforms of thecorrelation device output with respect to each reference symbol;

FIG. 15 is a schematic diagram illustrating the difference ofcorrelation device output waveforms;

FIG. 16 is a schematic diagram showing a flow of the generalsynchronizing operation and the OFDM demodulation operation;

FIG. 17 is a schematic conceptual diagram showing the construction ofreference symbol using the series A according to the present invention;

FIG. 18 is a schematic diagram showing waveforms of the reference symbolof the series (1);

FIG. 19 is a schematic diagram showing waveforms of the correlationdevice output with respect to the reference symbol of the series (1);

FIG. 20 is a schematic conceptual diagram showing the construction ofreference symbol using the series B according to the present invention;

FIG. 21 is a schematic diagram showing waveforms of the reference symbolof the series (2);

FIG. 22 is a schematic diagram showing waveforms of the correlatoroutput with respect to the reference symbol of the series (2);

FIG. 23 is a schematic diagram showing the difference of correlationoutput waveforms;

FIGS. 24A and 24B are schematic diagrams illustrating the electric powerwaveforms of the reference symbol;

FIG. 25 is a block diagram showing the circuit construction of atransmitter;

FIG. 26 is a block diagram showing the construction of a sync symbolinsertion circuit;

FIG. 27 is a block diagram showing the construction of a sync patternphase-shift circuit;

FIG. 28 is a block diagram showing the construction of a multiplier;

FIG. 29 is a block diagram showing the circuit construction of areceiver;

FIG. 30 is a block diagram showing the construction of a synchronizingcircuit;

FIG. 31 is a block diagram showing the construction of a timingsupplement circuit;

FIG. 32 is a block diagram showing the circuit construction ofreceiver/transmitter;

FIG. 33 is a block diagram illustrating the network configuration of thewireless home link;

FIGS. 34A and 34B are schematic conceptual diagrams showing theconstruction of reference symbol using the series A according to theother embodiment; and

FIGS. 35A and 35B are schematic conceptual diagrams showing theconstruction of reference symbol using the series B according to theother embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENT

Preferred embodiments of this invention will be described with referenceto the accompanying drawings:

(1) Theorem

The same repetition units as the conventional ones, series A and seriesB, will be used. By using the specific repetition pattern in therepetition pattern of the series A, the correlation detection patterndifferent from all conventional reference symbols can be obtained. Thus,in the case of differentiating the digital communication system by thereceiver, distinction becomes possible at once when detecting thereference symbol without demodulating the signal by the OFDM system.

More specifically, new code repetition patterns using the conventionalseries A and series B are as follows:“IA-A-IA-A-A-IA-A-IA-IA-C16-C64-C64” (reference symbol used the seriesA), and

-   “IB-IB-IB-IB-B-B-B-B-IB-C16-C64-C64” (reference symbol used the    series B).

The combination of these 2 types obtains the correlation outputcharacteristics different from the conventional pattern. In thefollowing explanations “IA-A-IA-A-A-IA-A-IA-IA-C16-C64-C64” will bereferred to as the series (1) and “IB-IB-IB-IB-B-B-B-B-IB-C16-C64-C64”will be referred to as the series (2). These are formed of 14.4microsecond and (for 4 symbols) of OFDM symbol of 72 samples.

As the feature of these series (1) and series (2), in the series (1),only series A is used as the repetition units and the series B is notused. Contrary to this, in the series (2), only series Bs are used. Inthis connection, IA means the signal waveform of the phase-shifted syncpattern A. Moreover, IB means the signal waveform of the phase-shiftedsync pattern B.

Furthermore, the series C makes the LSI operable by using the samewaveform as the other system.

(2) Signal Analysis of Reference Symbol

Firstly, the signal analysis result of the reference symbol of theseries (1) will be explained. The input pattern of the series (1) intothe IFFT is the same as shown in EQUATION (4), and its output waveformconsists of 64 samples as shown in FIGS. 17 and 18. And its waveform hasthe waveform formed of A-IA-A-IA, and A signal consisting of 16 samplesand the following shifted A, i.e., IA, appear alternately. The referencesymbol of the series (1) is formed of these signals combined.

Moreover, as shown in FIG. 19, 2 peak waveforms appear in the outputwaveform of the correlation circuit. As is clear from the waveform ofthe middle stage, codes of the real part of the correlation circuit areminus at these 2 peaks and 0 on the imaginary part. That is, the phaseis constantly 180° and this does not change. Accordingly, this can beclearly distinguished from the sync signal of the other system.

Next, the signal analysis result of the reference symbol of the series(2) will be explained. The input pattern of the series (2) into the IFFTis as shown in EQUATION (5), and as shown in FIGS. 20 and 21, its outputwaveform consists of 64 samples. And its waveform has the waveformformed of B-B-B-B, and B signal consisting of 16 samples will appearrepeatedly. The reference symbol of the series (2) is formed of thesesignals combined.

Furthermore, as shown in FIG. 22, 2 peak waveforms appear in the outputwaveform of the correlation circuit. As is clear from the waveform ofthe middle stage, codes of the real part of the correlation circuit areplus at 2 peaks, and the imaginary part is 0. That is, the phase isalways 0 and constant and it does not change. Accordingly, this can beclearly distinguished from the sync signal of the other system.

Thus, as is apparent from FIG. 25, the series (1) and the series (2) canbe distinguished.

FIGS. 24A and 24B show waveforms of the reference symbol signal. FIG.24A is the momentary electric power waveform of the series A, and FIG.24B is the momentary electric power waveform of the series B. Thetransversal axis shows the sample number 8 times over sampled, and thevertical axis shows the electric power normalized by the averageelectric power by dB. The maximum value of the vertical axis shows thepeak average ratio. The first half part is approximately 2 dB, and thelatter half part corresponding to the series C is approximately 3 dB.Since the first half part of the signal will be used for inputting theautomatic gain control (AGC), the peak average peak ratio (PAPR) is keptin sufficiently low value. The dynamic range of the first half part isapproximately 5 dB in FIG. 24A and 7 dB in FIG. 24B.

(3) Construction of Transmitter

Next, a transmitter to which these techniques are applied will bedescribed referring to drawings. FIG. 25 is a block diagram showing thedetailed construction of a transmitter capable of correctlysupplementing the timing according to the present invention.

As shown in FIG. 25, this transmitter is equipped with a channel encoder11, and data to be transmitted (hereinafter referred to as transmissiondata) will be supplied to the channel encoder 11, and outputs of thischannel encoder 11 will be supplied to a sync symbol insertion circuit20.

As shown in FIG. 26, the sync symbol insertion circuit 20 is equippedwith a multiplexer 21 and a memory 11. The multiplexer 21 inserting thereference symbol read out from the memory 22 into the encodedtransmission data to be given from the channel encoder 11, supplies thisto the orthogonal frequency division multiplexing (OFDM) burst formingcircuit 12.

The OFDM burst forming circuit 12 forms the burst frames in the OFDMsystem from the transmission data in which the reference symbol isinserted and supplies this to the inverse fast Fourier transform (IFFT)circuit 13. The IFFT circuit 13 conducts the inverse fast Fouriertransform to the transmission data burst-framed and supplies this to thesync electric power adjusting circuit 30.

The sync electric power adjusting circuit 30 increases the transmissionpower when sending the reference symbol as will be described later.Then, the output of the sync electric power adjusting circuit 30 will besupplied to the sync pattern phase-shift circuit 40.

As shown in FIG. 27, the sync pattern phase-shift circuit 40 is equippedwith a symbol counter 41, a phase-shifter 42, and a selector circuit 43.The symbol counter 41 detects the position of the predetermined syncpattern of the reference symbol and supplies this to the selectorcircuit 43.

The phase shifter 42, shifting the phase of the predetermined syncpattern, supplies to the selector circuit 43. The selector circuit 43,switching the sync pattern in which the phase of reference symbol isshifted to the other sync pattern of the same reference symbol, suppliesthis to the cyclic expansion insertion circuit 14.

The cyclic expansion insertion circuit 14, inserting the referencesymbol to the transmission data, supplies this to thein-phase/quadrature-phase (IQ) modulator 15. The IQ modulator 15, afterconverting the complex transmission data in which reference symbol isinserted to the real number transmission data (I series data and Qseries data), quadrature-phase modulating the carrier wave using thesedata, forms a radio frequency (hereinafter referred to as RF) signal andsupplies this to the TX (transmission) filter 16.

The TX filter 16, after filtering the RF signal in order to control theband, supplies this to the RF front end 17. Then, the RF front end 17transmits the RF signal.

Thus, in this transmitter, the reference symbol is inserted in thefrequency domain in order to avoid more complicated processings requiredin the case of inserting the reference symbol in time domain.

In this connection, the average electric power of the reference symbolis lower than the data symbol modulated by the OFDM system because thenumber of sub-carriers modulated is small.

Accordingly, the sync electric power adjusting circuit 30 increases thetransmitting electric power to conform to the average electric power ofdata symbol modulated by the OFDM system.

More specifically, the sync electric power adjusting circuit 30 isequipped with a multiplier 31 as shown in FIG. 28.

$\begin{matrix}{F_{pow} = \sqrt{\frac{N}{N_{sp}}}} & (7)\end{matrix}$

The sync electric power adjusting circuit 31 multiplies each sample ofthe reference symbol by the electric power adjusting coefficient Flowshown as above in EQUATION (7).

Then, after the electric power has been adjusted, the phase of thepredetermined sync pattern will be rotated for the fixed amount. Theamount of phase rotation is such as 180° rotation, and −1 is multiplied.

(4) Construction of Receiver

Next, a receiver according to the present invention will be described.FIG. 29 is a block diagram showing the detailed construction of areceiver according to the present invention.

This receiver comprises a RF front end 51, and the RF signal received atthe RF front end 51 is supplied to the IQ demodulator 52. The IQdemodulator 52 demodulates the RF signal and supplies the resultingcomplex data received to the synchronizing circuit 60.

As shown in FIG. 30, the synchronizing circuit 60 comprises a frequencysupplement circuit 61, frequency tracing circuit 62, timing supplementcircuit 70, timing tracing circuit 63 and the timing and frequencycorrection circuit 64.

Moreover, as shown in FIG. 31, the timing supplement circuit 70 isequipped with a delay circuit 71, a conjugate complex function device72, a multiplier 73, a delay circuit 74, an adder 75, a subtracter 76, adelay circuit 77 and a maximum detection circuit 78.

The delay circuit 71 delays the complex receive data from the IQdemodulator 52 for Nsp, i.e., for 1 sync pattern, and supplies to theconjugate complex function device 72. The conjugate complex functiondevice 72 supplies this to the multiplier 73 searching for the conjugatecomplex data of the complex receive data. And the multiplier 73multiplies the complex receive data by the conjugate complex data, i.e.,conducts the calculation of EQUATION (3) described above, and suppliesthe resulting multiplied data, i.e., the correlation value R(i) to thedelay circuit 74 and the adder 75.

The delay circuit 74 delays the multiplied data for the period shown inthe following EQUATION (8) and supplies this to the subtracter 76.(N−2*N _(sp))  (8)

The output data of the adder 75 is supplied to this subtracter 76. Andthe subtracter 76 subtracts the multiplied data delayed at the delaycircuit 74 from the output data, and supplies the resulting subtracteddata to the delay circuit 77 having the delay time of 1 unit and themaximum detection circuit 78.

The adder 75 adding up the multiplied data from the multiplier 73 andthe subtracted data delayed at the delay circuit 77, supplies this tothe subtracter 76 as described above. The maximum detection circuit 78obtains the sample position at which the output of the subtracter 76becomes the maximum and supplies this to the timing tracing circuit 63.

With this arrangement, the synchronization is trapped. The timingtracing circuit 63 monitors so that this trapped synchronism would notbe released.

Outputs of the synchronization circuit 60, such as the frame timingsignal showing the burst frame section and the packet synchronizingsignal showing the symbol timing are supplied to the fast Fouriertransform (FFT) circuit 53. And the FFT circuit 53 conducts the fastFourier transforms to the received data according to the timing signalof the synchronizing circuit 60 and supplies this to the OFDM burstresolving circuit 54.

The OFDM burst resolving circuit 54 removes the burst frame and makesthe data to bit stream and outputs this via the channel decoder 55.

More specifically, the synchronizing circuit 60, as well as calculatingthe timing and the offset of frequency to be brought in the receiveddata, corrects errors. The timing and frequency trapping algorithm isused for the initial synchronization at the beginning of the burstframe. On the other hand, the timing and the frequency tracing algorithmwill be used for maintaining the timing and frequency during the periodfrom the time when the timing and frequency are trapped to the timethese are renewed.

As described above, by changing the structure of reference symbolaccording to the present invention, the timing trapping accuracy can beremarkably increased. The maximum detection circuit 78 detects themaximum value of the correlation value R(i) of the reference symbolhaving renewed structure. And if the timing trapping would be conductedcorrectly, the frequency trapping can be conducted correctly.

According to the embodiment described above, the sync code series havingthe timing and frequency trapping functions, and selecting only thedigital communication system to which it belongs and reacting to thisnot synchronizing with the different digital communication system byselecting different sync code series has been shown.

(5) Construction of Digital Communication System

FIG. 32 is a block diagram showing the general construction oftransmitter/receiver to be used in the digital communication system.Here, the OFDM wireless communication system will be used as an exampleof the digital communication system. The transmitter 101 is equippedwith the functions described above in FIG. 25. The receiver 102 isequipped with the function described above in FIG. 29. The transmissionsignal and received signal are connected to an antenna 104 via anantenna for common use 103. The effects of the present invention in theOFDM wireless communication system in which the plural number of theOFDM transmitters/receivers are formed in network form will be describedin the following chapters.

FIG. 33 is a diagram showing the network in which the wireless home-linkand the digital communication system of BRAN are coexisted. In thisconnection, suppose that the waveform of the series (1) would be used asthe frame sync code series, and the waveform of the series (2) would beused as the packet sync code series.

One hub station 201 continuously transmits the reference symbol forframe synchronization at the cycle of 4 mm seconds and defines the frameboundaries of wireless home links. The hub station works as the networkcontrol station. The wireless transmitters/receivers other than the hubstation are called as leaf stations, and firstly these leaf stationsdetect the frame synchronizing signal from the hub station and find thecontrol station to which they themselves enter.

Suppose that the other system such as the BRAN system base station 203exists within the range this leaf station 202 can receive signal and iscontinuously transmitting the reference symbol for frame synchronizationdescribed above in FIG. 6.

In this case, for the leaf station of the wireless home link 202, thecontrol station to which it should enter is the hub station 201 and thebase station of the BRAN system is not the control station to which itenters. Thus, the leaf station identifies the reference symbol for framesynchronization of the hub station by using the correlation circuit thatit owns.

As described above in FIG. 12, in the correlation circuit, since outputwaveforms of the correlators are different each other as described abovein FIG. 19, FIG. 22 and FIG. 13B when the reference symbol for framesynchronization (1) of the wireless home link and the reference symbolfor packet synchronization (2) and the reference symbol for framesynchronization of the BRAN system are entered, the leaf station 202, bydistinguishing the waveform described above in FIG. 19, can know thetiming of frame boundary of the network to which it should entercorrectly.

Hereinafter, the control information transmitted from the controlstation 201 can be demodulated at the predetermined timing according tothe OFDM system and data exchange can be conducted.

On the other hand, since terminals of the BRAN, high speed wirelessaccess and IEEE802.11a can distinguish the reference symbol for framesynchronization and the reference symbol for packet synchronization ofthe wireless home link, they can receive signals mutually betweendifferent systems. However, they just detect the correlation of thereference symbol that exists at the start of the signal, they can judgewhether the signal is the signal that they should demodulate or not.

By demodulating the signal that is necessary for itself, the operationof the receiver becomes simple and the power consumption will bereduced, and the occurrence of erroneous operation of the system andmutual interference can be reduced.

(6) Operation and Effects of the Present Embodiment

According to the foregoing construction, in the digital communicationsystem, in the transmitter, after switching the sync pattern in whichreference symbol is phase-shifted to the other sync pattern of the samereference symbol and will be transmitted to the cyclic expansioninsertion circuit 14 from the sync pattern phase-shift circuit 40. Andin the cyclic expansion insertion circuit, after inserting the referencesymbols of the series (1) containing the structure of“IA-A-IA-A-A-IA-A-IA-IA” and/or the series (2) containing the structureof “IB-IB-IB-IB-B-B-B-B-IB” into the transmission data, thattransmission data will be transmitted.

Accordingly, in this digital communication system, since the referencesymbol having patterns different from the reference symbol is used inall conventional digital communication systems, the frame sync codeseries and/or the packet sync code series can be certainly identified.

Moreover, since the reference symbols will be generated by using theseries A, series B and the series C to be obtained by the IFFT, thedigital communication system can be identified by using the samecorrelation circuit as the conventional digital communication system. Inaddition to this, since the common circuit can be used when forming theshared device of the TEEE802.11a and the wireless home link by using thesame LSI, this is very convenient. And also the unit price reduction dueto the cost curtailment of the terminal parts and the effects of massproduction of LSI can be expected.

According to the foregoing construction, in the transmitter, switchingthe sync pattern in which the phase of reference symbol is shifted, andthe other sync pattern of the same reference symbol and the referencesymbol of the series (1) containing the structure“IA-A-IA-A-A-IA-A-IA-IA” and/or the series (2) containing the structureof “IB-IB-IB-IB-B-B-B-B-IB” are generated, and these are inserted intothe transmission data and to be transmitted, the frame sync code seriesand/or the packet sync code series can be certainly identified becausethe reference symbol having the pattern different from the referencesymbol used in all conventional digital communication systems. Thus,even when different communication systems exist mixed, the sync signalof the communication system in use can be certainly detected.

(7) Other Embodiments

The embodiment described above has dealt with the case of using thereference symbol of the series (1) and the series (2) in the digitalcommunication system of the OFDM system. However, the present inventionis not only limited to this but also the reference symbol can be used asthe sync signal of the radio communication system and the generaldigital communication system. And in this case the same effects as thoseof the embodiment described above can be obtained. Moreover, it can bealso used as sync signal in all radio communication systems not only inthe digital communication system of 5 GHz band.

Furthermore, the embodiment described above has dealt with the case ofusing the IFFT of 64 points. However, the present invention is not onlylimited to this but also the IFFT of other point number such as 256points can be used. And in this case, the same effects as those of theembodiment described above can be obtained.

Furthermore, the embodiment described above has dealt with the case offorming the phase structure of the sync pattern of the reference symbolusing the series A as “IA-A-IA-A-A-IA-A-IA-IA-C”. However, the presentinvention is not only limited to this but also the data series of whichthe phase is completely inverted “A-IA-A-IA-IA-A-IA-A-A-C”, or as shownin FIGS. 34A and 34B, “IA-A-IA-A-A-IA-A-IA-IA-X-C”,“X-IA-A-IA-A-A-IA-A-IA-IA-C” (where X shows an optional series such as Aor IA) can be used.

Furthermore, the embodiment described above has dealt with the case ofmaking the phase structure of the sync pattern of the reference symbolusing the series B as “IB-IB-IB-IB-B-B-B-B-IB-C”. However, the presentinvention is not only limited to this but also the data series of whichphase is completely inverted “B-B-B-B-IB-IB-IB-IB-B-C” or, as shown inFIGS. 35A and 35B, “IB-IB-IB-IB-B-B-B-B-X-C”,“X-IB-IB-IB-IB-B-B-B-B-IB-C” (where X shows an optional series such as Bor IB) can be used.

Moreover, the embodiment described above has dealt with the case ofmaking the data series of C domain as “C16-C64-C64”. However, thepresent invention is not only limited to this but also various combineddata series such as “C32-C64-C64”, “C32-C64”, or “C16-C64” and“C8-C64-C64”, and also “C8-C64” can be used as the data series of the Cseries.

Furthermore, according to the embodiment described above, the subcarrierof the series A has the value in every (4*i+2) order, making i asinteger. More specifically, this becomes “−22,−18, . . . ,−2,+2,+6, . .. ,+22”, or “−26,−22,−28, . . . ,−2,+2,+6, . . . ,+22,+26”. If thesecoefficients are entered into the IFFT, output waveforms of the IFFTalways become the form of “A-IA-A-IA”. Accordingly the value of SA ofthe series (1) is not only limited to the value described in EQUATION(4), but also the one that has the value every (4*i+2) order can beacceptable.

Furthermore, according to the embodiment described above, subcarrier ofthe series B has the value every (4*i) order making i as integer except0. More specifically, this becomes “−24,−20, . . . ,−4,+4,+8, . . .,+24”. If such coefficients are entered into the IFFT, the outputwaveform becomes always in the form of “B-B-B-B”. Accordingly, the valueof SB of the series (2) can be the value that has the value every (4*i)order not only the EQUATION (5) described above. In addition, thesub-carrier of the series B can be the one that has the value every(8*i) order, that is “−24,−16,−8,+8,+16+24” can be used.

According to the present invention as described above, since thetransmission data is encoded to the data symbol, the reference symbolsin which multiple sync patterns A and the phase-shifted sync pattern A,i.e., sync pattern IA, are aligned in time series in order to containthe structure of “IA-A-IA-A-A-IA-A-IA-IA ” is inserted to the datasymbol, and the data symbol in which the reference symbols are insertedis to be modulated to the radio frequency signal, the correlationdetection pattern remarkably different from the correlation detectionpattern of all conventional sync code series can be obtained. Thereby,when different communication systems exist mixed, the synchronizingsignal of the communication system in use can be detected certainly.

While there has been described in connection with the preferredembodiments of the invention, it will be obvious to those skilled in theart that various changes and modifications may be aimed, therefore, tocover in the appended claims all such changes and modifications as fallwithin the true spirit and scope of the invention.

1. A data modulation method comprising the steps of: encodingtransmission data into a data symbol; inserting into said data symbol areference symbol in which multiple synchronizing patterns are aligned ina time series in order to contain a structure ofIA-A-IA-A-A-IA-A-IA-IA (where: A is a synchronizing pattern and IA is aphase-shifted synchronizing pattern obtained by phase shifting A), saidreference symbol producing a waveform output having only two peaks whensaid reference symbol is input to a correlator of a receiver, therebyproducing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; and modulating thedata symbol in which said reference symbol is inserted with radiofrequency signals.
 2. The data modulation method according to claim 1,wherein said step of modulating the data symbol comprises conducting themodulation according to an orthogonal frequency division multiplexing(OFDM) system.
 3. A data modulation method comprising the steps of:encoding transmission data into a data symbol; inserting into said datasymbol a reference symbol in which multiple synchronizing patterns arealigned in a time series to contain a structure ofA-IA-A-IA-IA-A-IA-A-A (where: A is a synchronizing pattern and IA is aphase-shifted synchronizing pattern obtained by phase shifting A), saidreference symbol producing a waveform output having only two peaks whensaid reference symbol is input to a correlator of a receiver, therebyproducing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; and modulating thedata symbol in which said reference symbol is inserted with radiofrequency signals.
 4. The data modulation method according to claim 3,wherein said step of modulating the data symbol comprises conducting themodulation according to an orthogonal frequency division multiplexing(OFDM) system.
 5. A data modulation method comprising the steps of:encoding transmission data into a data symbol; inserting into said datasymbol a reference symbol in which multiple synchronizing patterns arealigned in a time series in order to contain a structure ofIB-IB-IB-IB-B-B-B-B-IB (where: B is a synchronizing pattern and IB is aphase-shifted synchronizing pattern obtained by phase shifting B) intosaid data symbol, said reference symbol producing a waveform outputhaving only two peaks when said reference symbol is input to acorrelator of a receiver, thereby producing a distinguishable waveformpattern from other waveform patterns produced by other communicationsystems; and modulating the data symbol in which said reference symbolis inserted with radio frequency signals.
 6. The data modulation methodaccording to claim 5, wherein said step of modulating the data symbolcomprises conducting the modulation according to an orthogonal frequencydivision multiplexing (OFDM) system.
 7. A data modulation methodcomprising the steps of: encoding transmission data in a data symbol;inserting into said data symbol a reference symbol into which multiplesynchronizing patterns are aligned in a time series in order to containa structure ofB-B-B-B-IB-IB-IB-IB-B (where: B is a synchronizing pattern and IB is aphase-shifted synchronizating pattern obtained by phase shifting B),said reference symbol producing a waveform output having only two peakswhen said reference symbol is input to a correlator of a receiver,thereby producing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; and modulating thedata symbol in which said reference symbol is inserted with radiofrequency signals.
 8. The data modulation method according to claim 7,wherein said step of modulating the data symbol comprises conducting themodulation according to an orthogonal frequency division multiplexing(OFDM) system.
 9. A data modulation device comprising: encoding meansfor encoding transmission data into a data symbol; reference symbolinsertion means for inserting into said data symbol a reference symbolin which multiple synchronizing patterns are aligned in a time series inorder to contain a structure ofIA-A-IA-A-A-IA-A-IA-IA (where, A is a synchronizing pattern and IA is aphase-shifted synchronizing pattern obtained by phase shifting A), saidreference symbol producing a waveform output having only two peaks whensaid reference symbol is input to a correlator of a receiver, therebyproducing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; and modulation meansfor modulating the data symbol in which said reference symbol isinserted with a wireless frequency signal.
 10. A data modulation devicecomprising: encoding means for encoding transmission data into a datasymbol; reference symbol insertion means for inserting into said datasymbol a reference symbol in which multiple synchronizing patterns arealigned in a time series in order to contain a structure ofIB-IB-IB-IB-B-B-B-B-IB (where, B is a synchronizing pattern and IB is aphase-shifted synchronizing pattern obtained by phase shifting B), saidreference symbol producing a two peak waveform output having only twopeaks when said reference symbol is input to a correlator of a receiver,thereby producing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; and modulation meansfor modulating the data symbol in which said reference symbol isinserted.
 11. A communication device comprising: encoding means forencoding transmission data into a data symbol; reference symbolinsertion means for inserting into said data symbol a reference symbolin which multiple synchronizing patterns are aligned in time series inorder to contain the structure ofIA-A-IA-A-A-IA-A-IA-IA (where: A is a synchronizing pattern and IA is aphase-shifted synchronizing pattern obtained by phase shifting A), saidreference symbol producing a waveform output having only two peaks whensaid reference symbol is input to a correlator of a receiver, therebyproducing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; modulation means formodulating the data symbol in which said reference symbol is insertedwith a radio frequency signal; an antenna for receiving/transmitting amodulated signal; and synchronization detection means for obtaining acorrelation value between the reference symbol of the modulated signalreceived and a delayed reference symbol and detecting a synchronization.12. A communication device comprising: encoding means for encodingtransmission data into a data symbol; reference symbol insertion meansfor inserting into said data symbol a reference symbol in which multiplesync patterns are aligned in a time series in order to include astructure ofIB-IB-IB-IB-B-B-B-B-IB (where, B is a synchronizing pattern and IB is aphase-shifted synchronizing pattern obtained by phase shifting B), saidreference symbol producing a waveform output having only two peaks whensaid reference symbol is input to a correlator of a receiver, therebyproducing a distinguishable waveform pattern from other waveformpatterns produced by other communication systems; modulation means formodulating the data symbol in which said reference symbol is insertedwith a radio frequency signal; an antenna for receiving/transmitting amodulated signal; and synchronization detection means for obtaining acorrelation value between the reference symbol of a modulated signalreceived and a reference symbol delayed and detecting synchronization.